1. Technical Field
The present invention relates to an optical projection system, which can perform conversion of the aspect ratio of a projected image, and a projector including the same.
2. Related Art
As a converter for aspect ratio conversion, which is used for the optical projection system of a projector, there is a front arrangement-type converter which is arranged to advance and retract in the front of an optical projection system in the related art, that is, in the front of an image side.
However, this type of converter is provided as an external optical section which is independent from the projector main body, causes an increase in the size of the projector, complicates the adjustment of the whole optical projection system including the converter, or badly degrades an image.
In addition, instead of the optical projection system of the projector, as a converter for aspect ratio conversion used in an imaging optical system, such as a camera, there is a rear arrangement-type relay system which is detachably arranged in the image side of an image forming optical system (refer to JP-A-2005-221597 and JP-A-2005-300928). This relay system includes a first group, a second group, and a third group. Among them, the intermediate second group is an anamorphic converter, and can be inserted into or retracted from between the first group and the third group.
However, the relay system or the anamorphic converter disclosed in JP-A-2005-221597 or the like is used in an imaging optical system. If the relay system or the anamorphic converter is used in an optical projection system as it is, various types of restrictions occur.
For example, in the case of the above-described rear arrangement-type relay system, the telecentricity is not considered. In such a relay system, in principal it is difficult to achieve both the telecentricity of a lateral section and the telecentricity of a longitudinal section. Therefore, if the telecentricity is precisely secured in one direction of an X section and a Y section, the telecentricity is greatly degraded in the remaining direction, so that the usage efficiency of light deteriorates or is biased according to the direction.
Further, in the imaging optical system disclosed in JP-A-2005-221597, it is fundamentally assumed that lenses can be replaced. When a rear arrangement-type relay system is not used, an image forming optical system is directly fixed to an imaging section and independently used. Therefore, in the case of maintaining the performance of the image forming optical system, there is a problem in that the length of the rear arrangement-type relay system becomes long. Meanwhile, lenses are not generally replaced in an optical projection system, so that a function as a general-purpose relay system or a general-purpose converter, in which various types of interchangeable lenses can be mounted, is not necessary.